This application is based upon and claims priority of Japanese Patent Application No. Hei 11-14554, filed, the contents being incorporated herein by reference.
The present invention relates to a solder bonding method, and an electronic device and a process for fabricating the electronic device, more specifically to a solder bonding method using a solder material containing Sn as a main component, and an electronic device and a process for fabricating the electronic device.
Recently, in view of the high-speed operation of semiconductor devices, techniques for short wiring lengths have been required. What is noted is flip chip bonding in which specifically solder bumps formed on a semiconductor chip are mounted on a circuit substrate with electrodes formed on, and are melted by heating for bonding.
The solder bonding method by the conventional flip chip bonding will be explained with reference to FIG. 4.
First, an electrical wiring 111 is formed of an Al film on a semiconductor substrate 110 with a prescribed device. Next, an electrode 116 is formed of a Ti film, an Ni film 113 and an Au film 114 on an electrical wiring 111, and a solder bump 118 is formed on the electrode.
On the other hand, an electrode 130 is formed of a Cr film 122, a Cu film 124, an Ni film 126 and an Au film 128 on an alumina substrate 120 with a prescribed circuit. Thus, the circuit substrate 132 with the electrode 130 formed on is formed.
Then, the solder bump 118 on the semiconductor substrate 110 is aligned with the electrode 130 on the circuit substrate 120, and is heated for the flip chip bonding. Such flip chip bonding makes the connection by means of lead wires unnecessary. The wiring length can be short.
Conventionally, Pbxe2x80x94Sn (Pb: lead, Sn: tin)-based solder materials have been widely used in the flip chip bonding. However, the Pb contained in Pbxe2x80x94Sn-based solder materials have isotopes, and the isotopes are intermediate products or terminal products of the decay series of U (uranium) and Th (thorium). Uranium (U) and thorium (Th) decay by the emission of He (helium), the solder materials emit a-rays. The xcex1-rays affect the operations of semiconductor devices, often causing the so-called soft errors. In a case that Pb flows into soil, the Pb is solved by acid rain, often affecting environments. From the ecological viewpoint, solder materials containing Pb as a non-main component are required.
As a solder material which replaces the Pbxe2x80x94Sn-based solder materials, solder materials containing Sn as a main component is noted.
However, in a case that a solder material containing Sn as a main component is used, because the Ni and Cu in the electrodes 116, 130 are reactive to the Sn in the solder bump 118, heat applied by the flip chip bonding produces metal compounds, etc., such as Nixe2x80x94Sn, Cuxe2x80x94Sn, etc. When the Ni reacts to the Sn, and the Ni film 113 is lost, it is difficult that the bonding between the solder bump 118, and the electrodes 116, 130 can be satisfactory because the Ti film 112, for example, and the solder bump 118 are incompatible with each other. In reliability test, such as a heat-cycle test, etc., the bonding was defective, and conduction, etc. are unsatisfactory. The reliability is poor.
An object of the present invention is to provide a solder bonding method, and an electronic device and a process for fabricating the electronic device, which make the bonding satisfactory even by the use of a solder material containing Sn as a main component.
The above-described object is achieved by a solder bonding method comprising the step of solder bonding a first electrode to a second electrode having a solder bump of mainly Sn on an upper surface thereof, the first electrode and/or the second electrode including a metal layer of an alloy layer containing Ni and P, an alloy layer containing Ni and B, or an alloy layer containing Ni, W and P. The metal layer of an alloy layer containing impurities, such as P, etc. can prevent the Ni of the metal layer from combining with the Sn in the solder bump. Accordingly, good bonded states can be obtained.
The above-described object is achieved by a solder bonding method comprising the step of solder bonding a first electrode to a second electrode having a solder bump of mainly Sn formed on an upper surface thereof, the first electrode and/or the second electrode including a metal layer of mainly Ni, and the solder bonding step being followed by the step of heat treating the alloy layer. The heat treatment can crystallize the metal layer, whereby the Ni of the metal layer can be prevented from combining with the Sn in the solder bump.
The above-described object is achieved by an electronic device comprising a first substrate including a first electrode, a second substrate including a second electrode having a solder bump of mainly Sn formed on an upper surface thereof, the first electrode and the second electrode being solder bonded to each other, the first electrode and/or the second electrode including a metal layer of an alloy layer containing Ni and P, an alloy layer containing Ni and B, or an alloy layer containing Ni, W and P. The metal layer of an alloy layer containing impurities, such as P, etc. can prevent the Ni of the metal layer from combining with the Sn in the solder bump. Accordingly, good bonded states can be obtained. Electronic devices having good bonded states can be provided.
The above-described object is achieved by an electronic device fabrication process comprising the step of solder bonding a first electrode formed on a first substrate to a second electrode which is formed on a second substrate and has a solder bump of mainly Sn formed on an upper surface thereof, the first electrode and/or the second electrode including a metal layer of an alloy layer containing Ni and P, an alloy layer containing Ni and B, or an alloy layer containing Ni, W and P. The metal layer of an alloy layer containing impurities, such as P, etc. can prevent the Ni of the metal layer from combining with the Sn in the solder bump. Accordingly, a process for fabricating electronic devices having good bonded states can be provided.
The above-described object is achieved by an electronic device fabrication process comprising the step of solder bonding a first electrode formed on a first substrate to a second electrode which is formed on a second substrate and has a solder bump of mainly Sn formed on an upper surface thereof, the first electrode and/or the second electrode including a metal layer of mainly Ni, and the step of heat treating the metal layer being followed by the solder bonding step. The heat treatment can crystallize the metal layer, whereby the Ni of the metal layer can be prevented from combining with the Sn in the solder bump.